1. Field of the Invention
The present invention relates to a gateway and a method for controlling electric equipment connected to LAN (Local Area Network), through WAN (Wide Area Network). In particular, the present invention relates to the gateway and the method for controlling home information appliances (electric equipments) connected to home network, through the Internet.
2. Description of the Related Art
Recently, there are home information appliances equipped with LAN connection interface to be connected to home network. Thereby, data transmitting and receiving through LAN is enabled between these electric equipments. An electric equipment can be operated from other electric equipment. Also, the electric equipment can be connected to WAN such as the Internet, through a gateway connected to LAN. Thereby, the electric equipment can receive content data from WWW (World Wide Web) server connected to the Internet.
Network layer of LAN and network layer of WAN are usually IP (Internet Protocol). On the other hand, application layer of LAN is usually different from application layer of WAN. For example, in many cases, LAN uses UPnP (Universal Plug and Play), and WAN uses SIP (Session Information Protocol).
Not only electric equipments which are compliant with UPnP, but also electric equipments which are non-compliant with UPnP are connected to LAN of home network. For example, electric equipments such as Web camera and ECHONET (Energy Conservation and HOmecare NETwork) white goods are non-compliant with UPnP. Thus, there is a technique to make electric equipment which is non-compliant with UPnP correspond virtually to electric equipment compliant with UPnP, (refer to documents 1 and 2). Based on this technique, electric equipments which are non-compliant with UPnP can be discovered and operated from electric equipments which are compliant with UPnP.
Also, a gateway based on such a technical function can be connected between LAN and WAN. Thereby, electric equipments connected to LAN can be discovered and operated from electric equipments connected through WAN (refer to document 1).
[document 1] Mayuko Tanaka, Chiyo Ono, Hiroshi Yamashita, “home network technique aiming at simple security—seamless Plug & Play technique and digital content copyright guard technique—”, Hitachi criticism, November 2004
[document 2] Takeshi Saito, Masao Issiki, Kenichi Sakurada, Toshihiro Fujibayashi, “Toshiba network home electric appliances realizing various service fusion”, Toshiba review, Vol. 60 No. 7, 2005
[document 3] Japanese Patent Laid-Open No. 2004-208101
Generally, a packet for operating or controlling electric equipment connected to LAN includes access address in application layer. The access address is URL (Uniform Resource Locator), for example. The access address is usually the same network address. That is to say, it is an address available only in the same LAN. Thus, when this address is utilized in other LAN, it cannot be connected because network addresses are different.
Also, in some cases second electric equipment connected to second LAN receives a packet transmitted from first electric equipment connected to first LAN. In this case, the second electric equipment cannot reply to the source address of the packet. This is because the source address usually shows a network address of the first LAN.
Further, gateway connected to home network usually controls network layers. When the gateway admits passage of the address in the network layer, the access address of all electric equipments in the home network becomes known from the WAN side.